Metal carbonyls disproportionation

Metal carbonyl disproportionation reactions. The following example illustrates this method ... 

The nature of the solvent plays an important role. Metal carbonyls disproportionate in basic solvents (e.g., in DMF) to form ionic complexes in which metal atoms have a 2+ formal charge (scheme 10). The product compositions of identified by IR spectroscopy varied with the extent of the substitution by carbonyl groups ... 

Similarly, treatment of a hexane solution of (77-C5Me5)2TiCl with CO at room temperature gave the thermally unstable adduct (17-C5Me5)2Ti(CO)(Cl) (52) as evidenced by again a high energy metal carbonyl band at 2000 cm-1 (98). Complex 52 slowly disproportionated at... 

A number of metal carbonyls undergo disproportionation reactions in the presence of other coordinating ligands. For example, in the presence of amines, Fe(CO)5 reacts as follows ... 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Not all reactions leading to carbonylate anions require strong reducing agents. Some involve reduction of the meta by carbon monoxide already present in the metal carbonyl or disproportionation of the complex In fact, the first synthesis of u metal carbonylate involved the former procedure ... 

There have been several recent reports of the reduction of carbon dioxide to carbon monoxide by transition metal complexes. Maher and Cooper (2/) have reported that several metal carbonyl dianions can effect the disproportionation of C02 to metal bound carbon monoxide [Eq. (37)] with Li2C03... 

The method is limited by the tendency of some T1(I) metal carbonylates to disproportionate, even at low temperatures, e.g. (79),... 

Based on the foregoing experimental results, the versatility of metal carbonyls and their derivatives in their reactions with liquid NH3 may be summarized as follows (/) substitution of CO or other ligands by NH3 without change in the oxidation number of the transition metal in question (2) conversion of covalent carbonyl complexes into ionic compounds by addition of NH3 molecules (3) base reactions" in which the transition metal is reduced to a carbonyl metalate with complementary oxidation of a CO ligand to CO(NH2)2 (4) valence disproportionations with... 

Since 1948-50, by using as reactants isonitriles, phosphorus trihalides, and tertiary phosphines, we have gained important insight into the dependence of reactions of metal carbonyls with bases upon the nature of the ligand. Organophosphines were introduced into carbonyl chemistry even prior to 1948 by Reppe and Schweckendiek (7). In general, these ligands react only by substitution of CO, and do not cause disproportionation. Thus nickel carbonyl frequently reacts with complete displacement of carbon monoxide, as we were first able to demonstrate in the reaction with phenyl isonitrile (8). 

The most common synthetic method (Fe, Ru, Os) is via pyrolysis of noncarbide metal carbonyl derivatives. It seems probable that the high temperature (140°-260°C) is not only responsible for formation of coor-dinatively unsaturated species and related condensations but also for the necessary disproportionation of carbon monoxide (58) ... 

Fe2(CO)9, and Fe3(CO)12, respectively. Similar disproportionations occurred with Ni(CO)4 and Co2(CO)8 which gave anionic species such as [Ni2(CO)6]2, [Ni3(CO)8]2, [Co(CO)4] , etc., upon treatment with ammonia or other amines. In contrast to the carbonyls of iron, nickel and cobalt, those of chromium, molybdenum and tungsten reacted with pyridine and 1,2-ethylenediamine to afford substitution products of the general composition M(CO)6 (py) (n = 1, 2, and 3) and M(CO)4(en) with the metal remaining in the oxidation state zero [25], Mainly as the result of this work, Hieber became convinced that the metal carbonyls should be regarded as true coordination compounds, and the coordinated CO should not be considered a radical but a monodentate ligand like NH3, pyridine, etc. He held this view despite the criticism by several of his contemporaries [3, 19] and was very pleased to see that in most textbooks published after 1940 this view had been accepted. 

A special case of redox reaction commonly encountered with metal carbonyls is disproportionation in the presence of Lewis bases, as exemplified for Co2(CO)g (see equation 26). 

Redaction of (5) with alkali metal forms the green clnster anion Co6(CO)i5 , which can be further rednced to the red dianion Co6(CO)i4, and isolated as a potassinm salt. The latter clnster anion is an early example of the expanding family of highly rednced transition metal carbonyls, for example Na3Co(CO)3, where np to two CO gronps are replaced by two electrons each. Co6(CO)is is also the mainprodnct from valence disproportionation of Co2(CO)g in ethanol. Oxidation (or acidification) of the clnster anions gives Co6(CO)i6. 

In the presence of excess base, a number of metal carbonyl complexes disproportionate (equations 73 and 74). 

This route is used when the dinuclear complex does not exist. Other preparative routes to metal carbonyl anions include reactions with certain hard bases such as pyridines which promote disproportionation and reaction with OH"... 

The course of the reactions of metal carbonyls with nitrogen bases leading either to disproportionation or to carbonyl substitution has been recognized since the very early work on metal carbonyls Since that... 

A rare redox reaction carried out by ETC catalysis is the disproportionation of bimetallic metal carbonyl complexes such as [MoCp(CO)3]2 containing a metal-metal bond, in the presence of a two-electron donor such as PMc3. In this typical example, the reaction leads to the ion pair [Mo Cp(CO)2(PMe3)2][Mo°Cp(CO)2]. The photolysis of the dimer gives the 17-electron iron radical [Mo Cp(CO)3] re-... 

The metal-carbon cluster systems we have considered so far in the present chapter, like the carboranes considered in the previous chapter, have contained one or more skeletal carbon atoms occupying vertex sites on the cluster deltahedron or deltahedral fragment. We now turn to some molecular cluster systems in which hypercoordinated carbon atoms occupy core sites in the middle of metal polyhedra. Most are metal carbonyl carbide clusters of typical formulae Mj (CO)yC. Their carbide carbon atoms are incorporated within polyhedra, which in turn are surrounded by y carbonyl ligands. Such compounds, for which few controlled syntheses are available, have been found primarily among the products of thermal decomposition of polynuclear metal carbonyls Mj (CO)j, their carbide carbon atoms result from disproportionation reactions of carbonyl ligands (2 CO CO2 + C). 

Metal carbonyls of the 7. and 8. group can react with strong n-donors under disproportionation to ionic metal carbonylates in a so-called "base-reaction , e.g. Fe(CO)5 with pyridine 235>. 

Tl derivatives of metal carbonyl anions are generally stable when the anion is weakly basic, e.g. Co(CO)3[P(OPh)3] , whereas disproportionation to Tl derivatives and Tl° occur when it is more strongly basic, e.g. Mn(CO)i. ... 

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